This invention relates generally to an electrostatographic printing machine, and more particularly concerns an improved toner dispensing apparatus for use therein.
The art of electrostatographic printing includes both electrographic printing and electrophotographic printing. In these processes, an electrostatic latent image, which corresponds to the original document being reproduced, is recorded. Electrophotography achieves this by charging a photosensitive element having a photoconductive insulating layer to a substantially uniform potential. The charged photoconductive surface is exposed to a light image of the original document. As a consequence of this exposure, the charge is selectively dissipated in the irradiated areas in accordance with the light intensity reaching the photoconductive surface. This creates the electrostatic latent image thereon. Electrographic printing differs from electrophotographic printing only in that the electrostatic latent image is created without the use of photosensitive materials. Hence, the process of electrophotographic printing requires the use of a suitable photoconductor whereas electrography does not.
Development of the electrostatic latent image, in electrophotography and electrography, is accomplished by contacting the latent image with a developer mix. Generally, a suitable developer mix comprises dyed or colored thermoplastic particles, known in the art as toner particles, mixed with carrier granules, such as ferromagnetic granules. The toner particles and carrier granules are triboelectrically attracted to one another with the toner particles adhering to the outer surface of the carrier granules. As the developer mix contacts the latent image, the greater attractive force of the latent image causes the toner particles to transfer thereto from the carrier granules. The toner particles adhere to the latent image in image configuration.
It is apparent that during the development cycle, toner particles are depleted from the developer mix. Thus, additional toner particles must be furnished to the developer mix so as to maintain copy density at a substantially optimum level. It is evident that in order to produce an efficient printing machine, it is necessary to conveniently and effectively replenish the toner particles used in the formation of copies.
Hereinbefore, various techniques were employed to dispense toner particles into the developer mix. For example, U.S. Pat. No. 2,892,446 issued to Olden in 1959; U.S. Pat. No. 2,910,964, issued to Stavrakis et al., in 1959; and U.S. Pat. No. 3,134,849, issued to Frohbach et al. in 1964, all disclose various techniques for dispensing toner particles from a hopper while the hopper is being vibrated. Another technique is taught in U.S. Pat. No. 3,003,703 issued to Hunt in 1969. Hunt teaches the use of a reciprocating gate on the bottom of a toner dispenser to discharge particles therefrom. Finally, U.S. Pat. No. 3,389,863 issued to Eichorn in 1968 discloses a toner container adapted to dispense toner particles from a block of toner. A plurality of reciprocating blades are mounted in the bottom of the container. The block of toner is biased against the blades. The blades are bent in a honeycombed configuration to insure complete coverage of the toner block and are mounted in a pair of end blocks. As the blades move across the surface of the toner block, they produce a scraping action which removes portions of the toner material therefrom.
None of the foregoing patents describe an apparatus adapted to prevent the bridging and caking of toner particles in a toner dispenser employed in a low-volume printing machine. In low copy volume printing, the toner particles frequently bridge and cake over the openings in the container preventing toner particle dispensing. This frequently results in light copies and customer dissatisfaction. In the past, this condition has been corrected by periodically manually stirring the toner particles.
It is the primary object of the present invention to improve toner particle dispensing by preventing bridging and caking of the particles.